1. Field of the Invention
The present invention relates to subterranean cementing operations, and more particularly, to improved cement dispersants for cement compositions and methods of cementing in subterranean formations.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized in subterranean applications including but not limited to well completion and remedial operations. For example, in well applications, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and/or positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore. Hydraulic cement compositions are also used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks in holes in pipe strings, and the like.
Dispersants are often used in subterranean well cement compositions to facilitate mixing the cement composition. Such dispersants are extensively used, inter alia, to reduce the apparent viscosities of the cement compositions in which they are utilized to allow the cement composition to be pumped with less friction pressure and less horsepower. In addition, the lower viscosity often allows the cement composition to be pumped in turbulent flow. Turbulent flow characteristics are desirable, for instance, when pumping cement compositions into subterranean wells to more efficiently remove drilling fluid from surfaces in the well bore as the drilling fluid is displaced by the cement composition being pumped. The inclusion of dispersants in cement compositions is also desirable in that the presence of the dispersants may facilitate the mixing of the cement compositions and reduce the water required. This may be desirable because cement compositions having reduced water content are often characterized by improved compressive strength development.
A number of dispersing agents have been utilized heretofore in cement compositions, particularly in cement compositions used for primary and remedial cementing in subterranean wells. One of the most common cement slurry dispersants is a condensate product of sulfonated naphthalene and formaldehyde. Such dispersants are problematic, however, because they are not substantially biodegradable, and hence, do not meet the regulatory requirements in some countries for use as dispersants.
Another conventional cement composition dispersant is the condensation product of formaldehyde, acetone, and an alkali metal sulfite. One formulation of this conventional dispersant is commercially available under the trade designation “CFR-3” from Halliburton Energy Services, Inc., of Duncan, Okla. While this and other similar dispersants may function well as dispersants in cement compositions, they are often environmentally unacceptable for use in wells subject to more stringent environmental regulations. Their unacceptability in these environments stems from, inter alia, their inability to undergo complete biodegradation in the environment, which may result in undesirable environmental effects if either accidentally or intentionally released into the environment.